Marinate the tuna in the olive oil and lime juice for 30 mins to an hour, or longer if preferred.
Grill the steaks on a hot grill for 2 minutes each side.
Chop all the vegetables, and mix together the yoghurt with the horseradish cream.
Arrange the mixed greens on two plates, and top with sliced tuna, fennel, cucumber, coriander, shallots and avocado.
Stir through the yoghurt dressing and add a drizzle of flaxseed oil over the salad, as well as some cracked black pepper to taste.